Downlighter fixing in lath and plaster ceiling

[Socksitis]

I know this is not everyone's choice, but it is mine. I would appreciate advice on how best to fix a downlighter in a lath and plaster ceiling. I have heard of several different methods, including the use of hessian soaked in plaster of paris and fixed on the laths that have been cut around the light fitting.

What have others done?

 

[Flyfisher]

I've never tried such a thing myself but I figured that electricians must come across this sort of thing fairly frequently and found this discussion topic on the IET forum:
http://www.theiet.org/forums/forum/messageview.cfm?catid=205&threadid=7065

It predates LED technology so there is some concern about heat from lightbulbs being a potential fire risk, though I'd expect this to not to be the case these days if LED bulbs are used.

My favourite comment was this "Thanks for the replies sounds as like "the building work" side of the job is going to more costly than the electrical". In my amateur experience of electrical work, this is pretty much always the case! :lol:

There's a 2013 thread on another forum here that says more or less the same thing while confirming that LEDs shouldn't be a fire risk:
https://talk.electricianforum.co.uk/topic/22053-downlights-in-lath-and-plaster/

 

[fernicarry]

Is the plaster of paris to hold the fitting in place or to stop the laths waggling around after you cut them?

I imagine the springy legs that normally hold the fitting up probably don't work terribly well with the thicker material in a lath and plaster ceiling.

I had to overboard (under-board?) our bathroom ceiling because the plaster was too unstable. I cut great big oversized holes in the old ceiling first so that the downlights only had to fit into the thickness of the plasterboard.

-Alan

 

[Abi Cott]

I've come across extension kits for the springy legs. Some of the lights sold by my employer come with them in the pack. I'm sure they would be available from an electrical specialist

 

[Socksitis]

I had to overboard (under-board?) our bathroom ceiling because the plaster was too unstable. I cut great big oversized holes in the old ceiling first so that the downlights only had to fit into the thickness of the plasterboard.

-Alan
[/quote]

Now that does sound an option

 

[Zebra]

Have done it many times, fit downlighters in lath and plaster. In principle it's no different to fitting them in a plasterboard ceiling. You cut yer 'oles, you stick 'em in. With a good sharp holesaw it's not difficult. But the act of cutting can loosen the nibs of the plaster from the laths, thereby it weakens the ceiling, and the lights then tend to droop with the weight. Also, if the ceiling is uneven it's hard to get them to sit right. Unevenness above is an issue too, if one spring has a lath to sit against and the other one has nothing but disintegrating plaster. They often droop one side. One thing you could do if you can get into the void above is fit small pieces of thin ply (if you're using LEDs - fire risk otherwise) for the springs to push into, so it doesn't weaken the ceiling.

 

[livias]

To avoid drooping and unevenness, cut away the plaster enough to expose the laths
Cut the hole out of the laths. A multitool.is your friend.
Cut spare pieces of lath long enough to straddle the raw ends at right angles so there will be a 'box' of lath around the light. Wiggle the lath bits into the hole. Drill and screw to fix
Make good with lime plaster
Job done